The present invention relates to an inverted telephoto lens.
Quite recently, of the interchangeable lenses for the 35 mm single lens reflex camera, there has been a tendency to make the wide angle lens, in particular, compact. On the other hand, for the wide angle lens for the single lens reflex camera, the inverted telephoto type lens is widely used, whereby a comparatively long back focus cn be obtained with this type of lens, which is advantageous. The lens system, however, is a symmetrical so that there are many difficulties in aberration correction.
Especially when the inverted telephoto type wide angle lens is made compact, what is most difficult is the correction of the distortion taking place in the divergent lens at the object side. For this aberration correction, it is effective to provide a positive lens in the divergent lens. In this respect, there are two representative constructions, namely the one where a negative lens is provided at the object side and a positive lens is provided behind the negative lens and the other where a positive lens and a negative lens are provided in sequence. When the above both constructions are compared with each other, the incident height and the incident angle of the axial light beam incident upon the positive lens effective for the distortion correction are large so that a larger correction effect for the distortion is obtained when the positive lens is provided frontmost in such a manner that it is effective to obtain a good correction with small total length.
However, when a positive lens is provided at the object side, the refractive force of the negative lens next to the positive lens becomes very strong so that the sagittal flare is greatly produced at this part, which phenomenon becomes very pronounced as the picture angle is increased. Further, the light beam out of the optical axis is refracted strongly with the positive lens so that it is pointed out that the lateral chromatic aberration has a tendency to become inferior while the diameter of the front lens has the tendency to become large.
The present assignee proposed with U.S. Patent Application Ser. No. 892,422 filed Mar. 31, 1978, now U.S. Pat. No. 4,188,092, an inverted telephoto type wide angle lens whose frontmost lens has a positive power in order to make the diameter of the frontmost lens smaller. As an embodiment of the above application, a lens having a picture angle of 84.degree., whose total length is 2.25 times as long as the focal length and whose F.No. is 1:2.0 is mentioned.
Following the above application, the present inventors proposed with Ser. No. 931,255 now U.S. Pat. No. 4,206,973 an inverted telephoto type lens whose total length is smaller though the F.No. is larger than that of the above embodiment.